Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand or DOD.
To smoothly transition between activated and deactivated modes, the internal combustion engine must produce torque with a minimum of disturbances. Otherwise, the transition will not be transparent to the driver. In other words, excess torque will cause engine surge and insufficient torque will cause engine sag, both of which degrade the driving experience.
Conventional engine control systems that provide torque smoothing have been based on brake torque and “as calibrated” spark. Engine control systems using this approach do not account for changes in engine and environmental conditions. This approach also does not meet drivability specifications for maximum torque disturbances allowed during transitions between activated and deactivated modes.